We have defined the cellular origin of basement membrane, discovered that injury to epithelial cells leads to increased synthesis of basement membrane, and in parallel with the experience with myelomas that synthesize monoclonal lines of immunoglobulin, we have isolated lines of tumors that make insoluble and soluble basement membrane molecules containing a common antigen. Accordingly, we propose to exploit this neoplastic system to: 1. determine if the soluble antigen is a fragment of the basement membrane molecule. 2. Derive monoclonal lines of the tumor to obtain homogeneous molecular species fit for molecular analyses. 3. Define the physiological function of basement membrane, and in particular how the basement membrane produced in disease affords protection to epithelial cells. 4. Study nephrosis as a disease involving basement membrane. Much speculation exists about the molecule, its function and role in disease; now we have the model and tools to do something about it.